Method and device for forming a dynamic pressure-generating groove in a fluid dynamic pressure bearing

ABSTRACT

An apparatus for forming a fluid dynamic pressure groove in a fluid dynamic pressure bearing including a mechanism for positioning and securing multiple workpieces to be machined to their respective machining devices; a mechanism for imparting an electrochemical dissolving effect to each target surface of the multiple workpieces to be machined, each of these workpieces serving as a part of the fluid dynamic pressure bearing; and a mechanism for forming at least one fluid dynamic pressure groove on each target surface of the multiple workpieces to be machined. The groove has a specified shape, dimension and surface condition. The same electrolyte is directed from a common electrolyte tank to each machining device used on the multiple workpieces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of and claims all rights ofpriority to U.S. patent application Ser. No. 10/636,150 filed Aug. 7,2003, which claims all rights of priority to Japanese Patent ApplicationSerial No. 2002-229437, filed Aug. 7, 2002 (pending).

FIELD OF THE INVENTION

The present invention relates to a method and device for forming a fluiddynamic pressure groove in a fluid dynamic pressure bearing used, forexample, as a high precision bearing in a hard disk drive device spindlemotor.

BACKGROUND OF THE INVENTION

Rapid development of memory storage devices achieved in recent yearsdemands an increase in recording density and capacity of such devices.This, in turn, requires an improvement in the device's track per inch(TPI) characteristic. In order to improve the TPI of a memory storagedevice, for example a hard disk drive, better performancecharacteristics, such as a spindle motor speed, rotational accuracy,noise level, shock resistance, etc., should be achieved. With respect tothe bearing systems utilized in hard disk drives, an improvement in arotational vibration and ability to withstand high-speed rotation hasbeen sought.

To respond to industry's demand for the improvement in rotationalvibration, ball bearing systems have been manufactured having rotatingelements made of materials having low adhesion and superior wearresistance. Specifically, ball bearing systems have been manufacturedwith rotating elements made of silicone nitride ceramics. Additionally,the machining accuracy of all bearing elements, i.e., the inner andouter rings and rotary members, is continued being improved upon.

The other known solution to the above demand for even greater speeds, isthe use of fluid dynamic pressure bearings as a replacement forconventional ball bearings. Fluid dynamic bearings are lower in noiseand allow to dramatically improve rpm speed of spindle motors used inhard disk drives.

In these fluid dynamic pressure bearings, a lubricating fluid (forexample, oil or air) is filled into a gap formed between a shaft and asupport member, typically a sleeve. Dynamic pressure generated in thelubricating fluid by a relative rotation of the shaft and the supportmember causes the shaft to be suspended away from the inner walls of thesupport member, thus forming a hydrodynamic bearing.

To facilitate generation of the hydrodynamic pressure and formation ofthe bearing, pressure-generating grooves may be provided the shaftand/or the support member. To form pressure-generating grooves, apattern of sideways V-shaped or herringbone-shaped grooves is etchedinto the bearing surface. In the formation of these sideways V-shapedpressure-generating grooves, an electrolytic machining method is used toform the requisite shape, dimensions and surface condition on therelevant workpiece surface by imparting an electrochemical dissolvingaction to the workpiece surface to be machined. Therefore, machiningaccuracy, improvement of productivity, efficiency, etc. of theelectrolytic machining method have become the new issues in the bearingmanufacturing process.

Here, before explaining the details of the electrolytic machiningmethod, we shall first briefly explain the structure of a spindle motorhaving a rotatable shaft supported for rotation by a fluid dynamicpressure bearing.

As shown in FIG. 5, spindle motor 01 is provided with rotor hub 03 thatrotates relative to base 02. Fluid dynamic pressure bearing 030 isinterposed between base 02 and rotor hub 03. Rotary shaft 020 isvertically mounted to rotor hub 03 and is inserted into bearing sleeve031 secured to the inner perimeter surface of interior cylindrical wall014 of base 02. Lubricant is supplied to a sliding portion of bearingsleeve 031 and rotary shaft 020. When the shaft rotates, the fluiddynamic pressure is generated in the lubricant due to the action ofherringbone-shaped dynamic pressure-generating groove 033 formed on theinner surface of the sleeve 031. Formed dynamic pressure causes rotaryshaft 020 to float upward from bearing sleeve 031. Thrust plate 034 ismounted at the bottom of rotary shaft 020. Although not shown in detail,dynamic pressure-generating herringbone shaped grooves may be formed onthe upper end surface of a thrust ring 034 and/or the step surface ofbearing sleeve 031 which opposes this upper end surface. Further,herringbone-shaped dynamic pressure-generating grooves may be formed onthe lower end surface of the thrust plate and/or on the upper surface ofcounter plate 037 fit into the bottom end of bearing sleeve 031.Lubricant is supplied between the step of bearing sleeve 031 and theupper surface of thrust plate 034, and between the lower surface of thethrust plate and counter plate 037. When rotary shaft 020 rotates, thelubricant pressure rises due to the action of the (herringbone-shaped)dynamic pressure-generating groove, the thrust ring 034 mounted on therotary shaft 020 floats up from the counter plate 037, rotating in anon-contacting state in a position midway between the sleeve 031 stepsurface and the counter plate 037 inner surface, not contacting the stepsurface of the sleeve 031.

The electrolytic machining method used in the invention of thisapplication is a machining method for obtaining a specified shape,dimension and surface condition of a groove by concentrating or limitingthe electrolytic dissolving action on a specified part of a workpiece inthe course of machine forming the above-described dynamicpressure-generating groove.

Prior technology for this electrolytic machining method is depicted inFIG. 4. FIG. 4 is a diagram showing the overall construction of anelectrolytic machining device for the purpose of forming a dynamicpressure-generating groove on the inner perimeter surface of a hollowcylindrical workpiece (sleeve) OW used as a support member for a spindlemotor shaft.

A positive terminal of the machining pulsed power supply 012 isconnected to the workpiece OW, while a negative terminal is connected totool 016, such that a DC pulsed voltage is applied between machiningsurface 015 of the workpiece OW and tool 016.

Tool 016 is provided with electrode 017 having sideways V-shaped(herringbone shaped) projecting portions approximately corresponding inshape and dimensions to the grooves which will be formed on the targetsurface. The size of sideways V-shaped (herringbone shaped) projectingportions of electrode 017 is usually somewhat smaller than the size of adesired dynamic pressure-generating groove. Tool 016 with projectingelectrode 017 is inserted into the inner bore of the workpiece OW suchthat during electrolytic machining the electrode faces the targetmachining surface 015 across a tiny gap. Target machining surface 015will later form the inner circumferential surface of the bearing sleeve.The workpiece OW is accurately positioned for the electro-machiningprocess using stationary fixture 013 and is secured to machining bed 02.

Electrolyte 011 stored in an electrolytic tank 07 is directed to thetiny gap provided between target machining surface 015 of the workpieceOW and the outer surface of tool 016. Electrolyte 011 is configured soas to be supplied in a fixed amount to the provided tiny gap by pump 08through filter 09. Electrolyte 011 that has passed through this tiny gapis then returned to electrolytic tank 07. Returned electrolyte 011 isagain supplied through circulation by means of pump 08.

During electrolytic machining, pump 08 operates and electrolyte 011 iscontinuously supplied to the aforementioned gap from electrolyte tank07. Here, when electrolyte 011 passes through the gap between targetmachining surface 015 of the workpiece OW and tool 016, products ofelectrolysis mix into electrolyte 011. In electrolytic machining,current densities are extremely high and machining gaps are extremelysmall, so the occurrence of electrolytic products and heating ofelectrolyte 011 have a significant effect on the quality of machining.Thus, there is a danger that if these effects are not quickly removed,machining may not progress. It is therefore necessary for the flow speedof electrolyte 011 to be fast, and, while there may be variationdepending on machining conditions, it is generally desirable for theflow speed to be in the range of 2-10 m/sec. When the electrolysisproducts are sedimentary, recirculating electrolyte 011 should be usedonly after cleaning. To separate and remove electrolytic products fromthe electrolyte 011 in the electrolyte tank 07 centrifuging,precipitation, filtering, or a combination of all of these may be used.

In a device thus constituted, current flows from the pulsed power supply012 and between the workpiece OW and tool 016 when a DC voltage (pulsedvoltage) is applied between the workpiece OW and tool 016 for aspecified time (electrolytic machining time). Assuming, for example,that the electrolyte is a sodium nitrate (NaNO₃) fluid and the workpieceOW surface is nickel (Ni), then primarily the following electrolyticreaction occurs:

-   Workpiece surface: Ni→Ni⁺⁺+2e⁻-   Tool surface: 2Na⁺⁼2H2O=2NaOH=H₂

When the workpiece OW is Fe, the following type of reaction occurs:

-   Workpiece surface: Fe→Fe⁺⁺+2e⁻    -   Fe⁺⁺=2OH⁻→Fe(OH)₂-   Tool surface: 2H⁺+2e⁻→H₂

In this type of reaction, the surface material of the workpiece OWfacing tool 016 dissolves in the electrolyte 011, and a dynamicpressure-generating groove having a shape corresponding to theprojecting pattern of the projecting electrode 017 is formed on targetmachining surface 015 of the workpiece OW.

During electrolytic machining, the current flowing between the workpieceOW and the tool 016 is controlled to be turned off and on as necessaryfor electrolytic machining. The shape and dimensions of the desireddynamic pressure-generating groove are determined by setting machiningconditions such as the size of the gap between target machining surface015 of the workpiece OW and tool 016. Other electrolytic machiningconditions that may influence the shape and dimensions of the groovesinclude the material of the workpiece OW, the applied current (A) andthe pulsed voltage application time (T). A dynamic pressure-generatinggroove of the required shape is thus formed in target machining surface015 of the workpiece OW.

In currently utilized electro-machining processes, a different machiningbed, electrolyte tank, and pulsed power supply have to be provided foreach workpiece type. Therefore, it is currently not possible to line upworkpieces of the same type or differing types and machine themsimultaneously. Therefore, machining has to be performed one item at atime, resulting in poor productivity. It is also currently necessary toadjust settings for each workpiece type that is very time consuming.Furthermore, each time the shape of the workpiece or the shape of thedesired dynamic pressure-generating groove is changed, additional timeis required for changeover to set the new precise gap width. Therefore,from a productivity and cost standpoint, market demands are notadequately met by currently available electro-machining methods.

An individually set up electrolyte tank is erected on each machiningdevice, and, because electrolyte tanks differ from one machining deviceto another even for the same workpiece, machining similar workpieces ondifferent devices may take place under different electrolyteconcentrations and states of electrolyte deterioration. This means thatelectrolytic concentration has to be controlled separately for eachelectrolyte tank.

SUMMARY OF THE INVENTION

The invention of the present application proposes to solve the problemswith the conventional methods and devices utilized to form fluid dynamicpressure bearing dynamic pressure-generating grooves. Further, thepresent invention provides a method and device for forming fluid dynamicpressure bearing dynamic pressure-generating groove reducing the set-uptime for each of multiple workpieces and allowing to simultaneouslymachine multiple different workpieces with different machiningconditions, so that dynamic pressure-generating groove productivity isimproved, manufacturing cost is reduced, the machining accuracy ofelectrolytic machining performed on multiple workpieces is stabilizedand the quality of each formed dynamic pressure-generating groove isimproved.

In general, in a first aspect, the invention features a method forforming a fluid dynamic pressure groove in a fluid dynamic pressurebearing. The method is accomplished by initially positioning andsecuring multiple workpieces to be machined to their respectivemachining devices and imparting an electrochemical dissolving effect toeach target surface of the multiple workpieces, each of these workpiecesserving as a part of the fluid dynamic pressure bearing, and forming atleast one fluid dynamic pressure groove on each target surface. Eachgroove may have a specified shape, dimension and surface condition. Thesame electrolyte is directed from a common electrolyte tank to eachmachining device used on the multiple workpieces.

The invention, as described above, causes the same electrolytes to bedirected from a common electrolytic tank to each of multiple workpiecemachining devices. Therefore, when forming dynamic pressure-generatinggrooves of differing shapes on multiple workpieces of the same ordiffering types it is possible to use a common electrolytic tank and toreduce manufacturing equipment. It is also possible to supplyelectrolytes under the same conditions to multiple differing workpiecesand, by stabilizing electrolytic machining accuracy, to increasequality. In particular, when multiple workpieces are multiple componentsof the same finished product, it is possible to have uniform machiningaccuracy over the whole finished product, thus enabling improvedperformance.

According to this groove forming method, an electrolytic tank is used incommon, so the requirement to separately control each electrolyte tankas in the conventional method, is eliminated simplifying operationcontrol, improving the productivity and reducing manufacturing costs.

In the provided method for forming a pressure-generating groove, allmachining devices for multiple workpieces are located on a commonmachining bed, and machining is accomplished by a pulsed voltagesupplied from a machining pulsed power supply.

As a result, multiple workpieces can be simultaneously machined with acommon machining bed on a single machining unit (dynamicpressure-generating groove forming device), and when multiple workpiecesare multiple components of the same finished product, it is easy toconcentrate the required number of each of the component parts, so thatmanufacturing control is simplified. Controlling the settings forcombinations of electrolyte and pulsed voltage to take into accountconcentration conditions and states of deterioration of the sameelectrolyte is also made easier, as is quality control over the shape ofthe dynamic pressure-generating groove formed in the workpiece targetwork surface. From these standpoints, productivity can be increased aswell.

Further, in the method for forming a fluid dynamic pressure bearingdynamic pressure-generating groove, the pulsed voltage supplied from thepulsed power supply is controlled so as to be independently applied toeach of the multiple workpieces.

It is thus possible to set machining conditions for each separateworkpiece, thus enabling simultaneous manufacturing of differingworkpiece types with a common machining bed on a single piece ofmachining equipment (dynamic pressure-generating groove forming device).

There are cases in which the target machining surface of the workpieceon which the dynamic pressure-generating groove is to be formed is theoutside surface of a spindle motor rotary shaft. There are also caseswhen it is the inside surface of a sleeve which fits over and serves asbearing to the rotary shaft. Depending on the form of the spindle motor,there may be various shapes of workpiece which are targets formachining, but using the provided groove forming method, it is possible,when forming dynamic pressure-generating grooves of differing shapes ondifferently shaped workpieces, to independently set pulsed voltage andapplication time for each differently-shaped workpiece, and thereforethe demands described above can be easily satisfied.

In general, in a second aspect, the invention features a groove formingdevice having a means for positioning and securing multiple workpiecesto be machined to their respective machining devices; a means forimparting an electrochemical dissolving effect to each target surface ofthe multiple workpieces, each of said workpieces serving as a part ofsaid fluid dynamic pressure bearing; and a means for forming at leastone fluid dynamic pressure groove on said each target surface of saidmultiple workpieces to be machined, said groove having a specifiedshape, dimension and surface condition. The same electrolyte is directedfrom a common electrolyte tank to each machining device used on saidmultiple workpieces.

The invention, as described above, is such that the same electrolyte isdirected from a common electrolyte tank to each machining device formultiple workpieces, so that even when forming dynamicpressure-generating groove of differing shapes in multiple workpieces ofthe same and differing types, a common electrolyte can be used, andmanufacturing equipment can be reduced.

For multiple differing workpieces, electrolyte can be supplied under thesame conditions, thus enabling stabilization of the electrolyticmachining accuracy and improvement of quality. In particular, when themultiple workpieces are multiple parts of the same finished product,machining accuracy can be maintained through the entire finishedproduct, leading to improved performance.

As the common electrolyte tank can be used with this groove formingdevice, the need to separately control each electrolyte tank disappears,and operational control can be simplified, while productivity isincreased and manufacturing costs are reduced.

In the groove forming device set forth above, multiple machining devicesfor multiple workpieces are concentrated on a common bed, and machiningis carried out by a pulsed voltage supplied from a machining pulsedpower supply.

As a result, it is possible to simultaneously machine multipleworkpieces with a common machining bed on a single piece of machiningequipment (dynamic pressure-generating groove forming device), so thatwhen multiple workpieces are the multiple parts of the same finishedproduct, it is easy to assemble the numbers of each part, andmanufacturing control is made easier. Control over settings ofelectrolyte and pulsed voltage combinations which take into accountconcentration conditions and degree of degradation in the sameelectrolyte is also made easier, and quality control over the shape ofthe dynamic pressure-generating groove formed in the workpiece targetmachining surface is simplified, as is quality control over the shape ofthe dynamic pressure-generating groove formed in the workpiece targetmachining surface. This aspect also permits an increase in productivity.

Further, in the groove forming device the pulsed voltage supplied fromthe pulsed power supply can be independently applied to each of themultiple workpieces. It is thus possible to set different machiningconditions for each workpiece, and to manufacture multiple typessimultaneously with a common machining bed on a single machine (dynamicpressure-generating groove forming device).

There are cases in which the target machining surface of the workpiece,in which the dynamic pressure-generating groove is to be formed, is theoutside surface of a spindle motor rotary shaft. There are also caseswhere it is the inner surface of a sleeve which fits over and serves asa bearing to the rotary shaft. Depending on the form of the spindlemotor, there may be various shapes of workpiece surfaces which aretargets for machining. Using the present groove forming device, it ispossible, when forming dynamic pressure-generating grooves of differingshapes on differently shaped workpieces, to independently set pulsedvoltage and application time for each differently-shaped workpiece, andtherefore the demands described above can be easily met.

The above aspects, advantages and features are of representativeembodiments only. It should be understood that they are not to beconsidered limitations on the invention as defined by the claims.Additional features and advantages of the invention will become apparentin the following description, from the drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by way of example and not limitation andthe figures of the accompanying drawings in which like references denotelike or corresponding parts, and in which:

FIG. 1 is a schematic diagram depicting construction of a device forforming a fluid dynamic pressure bearing dynamic pressure-generatinggroove in accordance with the first embodiment of the present invention.

FIG. 2 is a schematic diagram explaining the machining method of acylindrical rotary piece used in a fluid dynamic pressure bearing,wherein the surface to be machined is the inner circumferential surfaceof the rotary piece.

FIG. 3 is a schematic diagram explaining the machining method of acounter plate used in a fluid dynamic pressure bearing, wherein thesurface to be machined is the end surface of the counter plate.

FIG. 4 is a schematic diagram depicting the construction of aconventional electrolytic machining device for forming a fluid dynamicpressure bearing dynamic pressure-generating groove.

FIG. 5 is a cross-sectional view of a conventional spindle motor havinga rotary shaft supported by a fluid dynamic pressure bearing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS AND THE DRAWINGS

The present invention is explained with reference to one of itsembodiments, shown in FIGS. 1 through 3. In accordance with the presentembodiment, FIG. 1 depicts an overall construction of the device forforming dynamic pressure-generating grooves for a fluid dynamic pressurebearing. FIG. 2 illustrates a machining method used when the workpieceis a cylindrical rotary part which can later be used as a bearing sleevein a fluid dynamic pressure bearing, wherein the inner circumferentialsurface of the workpiece is the target machining surface.Finally,.Figure 3 illustrates a machining method used when the workpieceis a counter plate of a fluid dynamic pressure bearing, and the targetmachining surface is one of the end surfaces of the counter plate.

As shown in FIG. 1, multiple machining devices 3-1, 3-2, 3-3, 3-4, . . .are aligned on machining bed 2 in the groove forming device of thepresent embodiment. Depending on particulars of a specific manufacturingprocess, these machining devices 3-1, 3-2, 3-3, 3-4 can be differentmachining devices or multiple units of the same machining device.

If necessary, all of these units may be simultaneously used for formingpressure-generating grooves. Alternatively, only some of the units maybe selectively turned on. In the present embodiment, machining devices3-1 and 3-2 are the same machining devices that perform the machining ofan inner surface of the cylindrical rotary part. They are moreparticularly shown prior to implementation of machining in FIG. 2. Inthe present embodiment, machining devices 3-3 and 3-4 are the samemachining devices that perform the machining of a surface of the counterplate. They are more particularly shown prior to implementation ofmachining in FIG. 3.

Broadly divided, machining devices 3-1, 3-2, 3-3, 3-4 respectivelyinclude support fixture portions 4-1, 4-2, 4-3, 4-4 which support andaffix workpieces W1, W2, W3, W4; electrolyte supply portion 5 requiredfor electrolytic machining; and electrode portions 6-1, 6-2, 6-3, 6-4applying pulsed voltages.

Here, requisite fixtures are arrayed on the same machining bed 2 inaccordance with the shape of workpieces W1, W2, W3, W4, for example,spindle motor rotary shaft, counter plate, etc., as the fixtures 13-1(FIG. 2), 13-2, 13-3 (FIG. 3), 13-4 used in the fixture portions 4-1,4-2, 4-3, 4-4.

In the electrolyte supply portion 5, a common electrolyte tank 7 is usedwith respect to all of the machining devices 3-1, 3-2, 3-3, 3-4 andelectrolyte 11 is supplied to each machining device 3-1, 3-2, 3-3, 3-4from electrolyte tank 7 by pump 8 through filter 9 and splitterjunction) valve 10. The speed of electrolyte fluid 11 flowing to eachelectrolytic machining portion of machining devices 3-1, 3-2, 3-3, 3-4can be adjusted by setting pump 8 and splitter junction) valve 10 toobtain the necessary electrolytic machining performance. Also, while notillustrated, junction valve 10 is constructed so as to be electricallycontrollable so that the required flow quantity of electrolyte 11 issupplied respectively to machining devices 3-1, 3-2, 3-3, 3-4.Electrolyte 11, which has passed through each electrolytic machiningportion of machining devices 3-1, 3-2, 3-3, 3-4 and recovered the metalions produced by electrolytic machining, is returned to electrolyte tank7 through the recovery line.

Electrode portions 6-1, 6-2, 6-3, 6-4 correspond to the tool holdinghead in a machine tool. Negative terminals of the pulsed power supply 12are connected to the tool holding heads, while positive poles areconnected to workpieces W1, W2, W3, W4. Appropriate pulsed voltages arerespectively applied between electrode portions 6-1, 6-2, 6-3, 6-4 andworkpieces W1, W2, W3, W4. These pulsed voltages are applied in thepredetermined pulsed voltage amounts and at the required time to theappropriate machining device for the electrolytic machining to beperformed in machining devices 3-1, 3-2, 3-3, 3-4.

FIG. 2 shows an expansion of the pre-machining state of machiningdevices 3-1, 3-2 shown in FIG. 1. Although, the explanation below refersonly to the machining device 3-1, it is equally applicable to the device3-2.

Mounting part 13-1 of fixture portion 4-1 is located on the commonmachining bed 2 to accurately position, support and hold securelyworkpiece W1. As shown in FIG. 2, workpiece W1 is a rotary cylindricalmember (sleeve) integrated as one part with rotor hub 14 of spindlemotor. The inner cylindrical surface of the inner bore of the sleeve isthe target machining surface 15-1, and tool 16-1 of electrode portion6-1 is inserted into the bore so as to face this target machiningsurface 15-1. Tool 16-1 is supported by the base portion of electrodeportion 6-1 projecting downwardly therefrom. Projecting electrodeportions 17-1 are formed at 2 positions, top and bottom, of the outercircumferential surface of the tip portion on the rod-shaped electrodeportion 6-1. Projecting electrode portions 17-1 include a projectingpattern of sideways Vs (or herringbone shaped protrusions). Thissideways V-shaped pattern on projecting electrode portion 17-1 istransferred to target machining surface 15-1 of the cylindricalworkpiece W1 by electrolytic machining.

A high degree of accuracy is sought for the dimension of the gap portionbetween projecting electrode portion 17-1 and target machining surface15-1 of the. workpiece W1. Therefore, the relative positionalrelationship between the workpiece W1 and tool 16-1 is set with highprecision. Any groove pattern required for a particular fluid dynamicbearing may be set as the pattern of projecting electrode portion 17-1.For example, sideways V-shaped grooves, herringbone. grooves, asymmetricgrooves or any other appropriate groove pattern can be utilized.

Electrolyte 11 supplied from common electrolyte tank 7 is set so that itflows through the gap portion with a fixed flow rate. Metal ionsproduced by the electrical decomposition induced by the pulsed voltageapplied between projecting electrode portion 17-1 and target machiningsurface 15-1 are quickly removed from target machining surface 15-1.Thus, the electrical decomposition is implemented continuously on targetmachining surface 15-1 during application of pulsed voltage, forming adynamic pressure-generating groove of the desired shape on targetmachining surface 15-1.

FIG. 3 shows an expansion of the pre-machining state of machiningdevices 3-3, 3-4 shown in FIG. 1. Although, the explanation below refersonly to the machining device 3-3, it is equally applicable to the device3-4.

Mounting part 13-3 of fixture portion 4-3 is located on the commonmachining bed 2 to accurately position, support and hold securelyworkpiece W3. In this embodiment, workpiece W3 is a counter plate usedin a fluid dynamic pressure bearing of a spindle motor. Target machiningsurface 15-3 is the end surface of the counter plate. This targetmachining surface 15-3 is accurately positioned with respect toprojecting electrode portion 17-3 provided on the lower end surface oftool 16-3 of electrode portion 6-3. The pulsed voltage is appliedbetween target machining surface 15-3 and projecting electrode portion17-3 inducing electrolytic machining of the target surface. The roleplayed by the electrolyte 11 is similar to the case of machining device3-1 shown in FIG. 2.

Because of the construction described above, the present invention canachieve the following types of effects.

The same electrolyte 11 is directed from a common electrolyte tank 7 toeach machining devices 3-1, 3-2, 3-3, 3-4 of the multiple workpieces W1,W2, W3, W4 and, therefore, even when forming dynamic pressure-generatinggrooves with differing shapes in multiple workpieces W1, W2, W3, W4 ofthe same or different types, a common electrolyte tank 7 may be used.Thus, manufacturing equipment requirements are reduced. It is alsopossible in the presently provided device to supply electrolyte 11 underthe same conditions to multiple different workpieces W1, W2, W3, W4, tostabilize electrolytic machining accuracy and to improve quality. Inparticular, where multiple workpieces W1, W2, W3, W4 are multiple partsof the same finished product, the same machining accuracy is maintainedthroughout the whole finished part and performance is improved.

According to the provided groove forming method and device, electrolytictank 7 is commonly used by all machining devices 3-1, 3-2, 3-3, 3-4.Therefore, there is no need to control each electrolyte tank separately,as was conventionally done, making operational control easier andpermitting improved performance and reduced manufacturing cost.

Additionally, because each machining device 3-1, 3-2, 3-3, 3-4 ofmultiple workpieces W1, W2, W3, W4 is disposed on common machining bed2, and machining is implemented by a pulsed voltage supplied frommachining pulsed power supply 12, multiple workpieces W1, W2, W3, W4 canbe simultaneously machined on the common machining bed 2 of a singlemachine (dynamic pressure-generating groove forming device 1). Whenmultiple workpieces W1, W2, W3, W4 are multiple parts of the samefinished product, it is easy to assemble the parts together simplifyingand improving the manufacturing control. Controlling the settings forcombinations of electrolyte and pulsed voltage to reflect concentrationconditions and states of deterioration of electrolyte 11 is alsosimplified by the current invention. Also, the quality control over theshape of the dynamic pressure-generating grooves formed in target worksurfaces 15-1, 15-2, 15-3, 15-4 of workpieces W1, W2, W3, W4 issimplified.

Pulsed voltages supplied from pulsed power supply 12 are controlled soas to be independently applied to multiple workpieces W1, W2, W3, W4.Therefore, differing machining conditions can be set for each workpiece,and many types of workpieces can be simultaneously manufactured on acommon machining bed 2 of a single machine (dynamic pressure-generatinggroove forming device 1).

Depending on the structure of the spindle motor, there may be variousshapes of workpieces which are targets for machining, but using thedescribed groove forming device, it is possible to independently setpulsed voltage and application time for each differently-shapedworkpiece W1, W2, W3, W4.

In the above described embodiments, the groove forming method and devicetherefore are described in their application to a spindle motor, butthey are not limited thereto. Wide application to other parts or devicesusing similar fluid dynamic pressure bearings is possible, and theinvention of the present application is not limited to theaforementioned embodiments. Various variations are possible within arange that does not depart from the essence of the invention of thepresent application.

For the convenience of the reader, the above description has focused ona representative sample of all possible embodiments, a sample thatteaches the principles of the invention and conveys the best modecontemplated for carrying it out. The description has not attempted toexhaustively enumerate all possible variations. Other undescribedvariations or modifications may be possible. For example, where multiplealternative embodiments are described, in many cases it will be possibleto combine elements of different embodiments, or to combine elements ofthe embodiments described here with other modifications or variationsthat are not expressly described. Many of those undescribed variations,modifications and variations are within the literal scope of thefollowing claims, and others are equivalent.

1. An apparatus for forming a fluid dynamic pressure groove in a fluiddynamic pressure bearing, comprising: a means for positioning andsecuring multiple workpieces to be machined to their respectivemachining devices; a means for imparting an electrochemical dissolvingeffect to each target surface of said multiple workpieces to bemachined, each of said workpieces serving as a part of said fluiddynamic pressure bearing; and a means for forming at least one fluiddynamic pressure groove on said each target surface of said multipleworkpieces to be machined, said groove having a specified shape,dimension and surface condition, wherein the same electrolyte isdirected from a common electrolyte tank to each machining device used onsaid multiple workpieces.
 2. The apparatus for forming a fluid dynamicpressure groove according to claim 1, wherein all machining devices usedon said multiple workpieces are located on a common machining bed, andwherein said means for imparting said electrochemical dissolving effectfurther comprise means for supplying a pulsed voltage from a pulsedpower supply.
 3. The apparatus for forming a fluid dynamic pressuregroove according to claim 2, wherein said pulsed voltage supplied fromsaid pulsed power supply is independently applied and controlled withrespect to each of said multiple workpieces.